Managing thermal budget in annealing of substrates

ABSTRACT

A method and apparatus are provided for treating a substrate. The substrate is positioned on a support in a thermal treatment chamber. Electromagnetic radiation is directed toward the substrate to anneal a portion of the substrate. Other electromagnetic radiation is directed toward the substrate to preheat a portion of the substrate. The preheating reduces thermal stresses at the boundary between the preheat region and the anneal region. Any number of anneal and preheat regions are contemplated, with varying shapes and temperature profiles, as needed for specific embodiments. Any convenient source of electromagnetic radiation may be used, such as lasers, heat lamps, white light lamps, or flash lamps.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 14/229,238, filed Mar. 28, 2014, is a continuation of U.S.patent application Ser. No. 12/212,157, each of which is hereinincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention relate to a method of manufacturing asemiconductor device. More particularly, embodiments of the inventionare directed to a method of thermally processing a substrate.

2. Background

The integrated circuit (IC) market is continually demanding greatermemory capacity, faster switching speeds, and smaller feature sizes. Oneof the major steps the industry has taken to address these demands is tochange from batch processing silicon wafers in large furnaces to singlewafer processing in a small chamber.

During such single wafer processing the wafer is typically heated tohigh temperatures so that various chemical and physical reactions cantake place in multiple IC devices defined in the wafer. Of particularinterest, favorable electrical performance of the IC devices requiresimplanted regions to be annealed. Annealing recreates a more crystallinestructure from regions of the wafer that were previously made amorphous,and activates dopants by incorporating their atoms into the crystallinelattice of the substrate, or wafer. Thermal processes, such asannealing, require providing a relatively large amount of thermal energyto the wafer in a short amount of time, and thereafter rapidly coolingthe wafer to terminate the thermal process. Examples of thermalprocesses currently in use include Rapid Thermal Processing (RTP) andimpulse (spike) annealing. While such processes are widely used, currenttechnology is not ideal for large substrates which tend to be exposed toelevated temperatures for a long time period. These problems become moresevere with increasing switching speeds and/or decreasing feature sizes.

In general, these thermal processes heat the substrates under controlledconditions according to a predetermined thermal recipe. These thermalrecipes fundamentally consist of a temperature that the semiconductorsubstrate must be heated to the rate of change of temperature, i.e., thetemperature ramp-up and ramp-down rates and the time that the thermalprocessing system remains at a particular temperature. For example, somethermal recipes may require the entire substrate to be heated from roomtemperature to a temperature of 400° C. or more for processing timesthat exceed the thermal budget of the devices formed on the substrate.

Moreover, to meet certain objectives, such as minimal inter-diffusion ofmaterials between different regions of a semiconductor substrate, theamount of time that each semiconductor substrate is subjected to hightemperatures must be restricted. To accomplish this, the temperatureramp rates, both up and down, are preferably high. In other words, it isdesirable to be able to adjust the temperature of the substrate from alow to a high temperature, or visa versa, in as short a time aspossible.

The requirement for high temperature ramp rates led to the developmentof Rapid Thermal Processing (RTP), where typical temperature ramp-uprates range from 200 to 400° C./s, as compared to 5-15° C./minute forconventional furnaces. Typical ramp-down rates are in the range of80-150° C./s. A drawback of RTP is that it heats the entire wafer eventhough the IC devices reside only in the top few microns of the siliconwafer. This limits how fast one can heat up and cool down the wafer.Moreover, once the entire wafer is at an elevated temperature, heat canonly dissipate into the surrounding space or structures. As a result,today's state of the art RTP systems struggle to achieve a 400° C./sramp-up rate and a 150° C./s ramp-down rate.

As device sizes on substrates grow smaller in the future, thermalbudgets must reduce as well, because smaller devices may be degradedmore easily by inter-diffusion of materials. Temperature ramp-up andramp-down rates must be increased to compress anneal times, for examplebelow one second.

To resolve some of the problems raised in conventional RTP typeprocesses, various scanning laser anneal techniques have been used toanneal the surface(s) of the substrate. In general, these techniquesdeliver a constant energy flux to a small region on the surface of thesubstrate while the substrate is translated, or scanned, relative to theenergy delivered to the small region. Other laser scanning processeshold the substrate still and move the laser across the substratesurface. Due to the stringent uniformity requirements and the complexityof minimizing the overlap of scanned regions across the substratesurface, these types of processes are not effective for thermalprocessing contact level devices formed on the surface of the substrate.Additionally, thermal stresses generated in the substrate by the highthermal gradients associated with extreme localized heating may resultin damage to the substrate.

In view of the above, there is a need for novel apparatuses and methodsfor annealing a semiconductor substrate with high ramp-up and ramp-downrates. This will offer greater control over the fabrication of smallerdevices leading to increased performance.

SUMMARY

Embodiments described herein provide an apparatus for thermally treatinga substrate, comprising a movable substrate support; a first energysource for directing annealing energy in a rectangular shape toward afirst portion of a surface of the substrate support; a second energysource for directing preheat energy in a tapered shape toward a secondportion of the surface of the substrate support; and an optical assemblyhousing the first and second energy sources.

Other embodiments provide an apparatus for thermally treating asubstrate, comprising a movable substrate support; a first energy sourcefor directing annealing energy in a rectangular shape toward a firstportion of a surface of the substrate support; a second energy sourcefor directing preheat energy in a triangular shape toward a secondportion of the surface of the substrate support; and an optical assemblyhousing the first and second energy sources.

Other embodiments provide an apparatus for thermally treating asubstrate, comprising a movable substrate support; a first energy sourcefor directing shaped annealing energy in a rectangular shape toward afirst portion of a surface of the substrate support; a second energysource for directing shaped preheat energy in a tapered shape toward asecond portion of the surface of the substrate support; and an opticalassembly housing the first and second energy sources.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1A is a schematic isometric view an apparatus according to oneembodiment of the invention.

FIG. 1B is a schematic bottom view of one embodiment of the energysource of FIG. 1A.

FIG. 2 is a schematic isometric view of an apparatus according toanother embodiment of the invention.

FIG. 3A is a graph of temperature versus position on a substrateundergoing a process according to one embodiment of the invention.

FIGS. 3B-3C are schematic top views of substrates undergoing processesaccording to two embodiments of the invention.

FIG. 4 is a schematic side view of an apparatus according to oneembodiment of the invention.

FIG. 5 is a schematic cross-sectional diagram illustrating a processingchamber according to an embodiment of the invention.

FIG. 6 is a schematic top view of a substrate undergoing a processaccording to one embodiment of the invention.

FIG. 7 is a schematic cross-sectional diagram illustrating a processingchamber according to an embodiment of the invention.

FIGS. 8A-8B are graphs of temperature versus time on substratesundergoing processes according to embodiments of the invention.

FIG. 9 is a flow diagram summarizing a method according to oneembodiment of the invention.

FIG. 10 is a flow diagram summarizing a method according to anotherembodiment of the invention.

FIG. 11 is a flow diagram summarizing a method according to anotherembodiment of the invention.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation.

DETAILED DESCRIPTION

As device dimensions on substrates grow smaller, and as substratesthemselves grow larger, it becomes increasingly impractical to performthermal treatment on entire substrates at one time. The power requiredto energize the entire surface grows prohibitive, as does theopportunity for non-uniform treatment. Thermal treatment tools such asRTP chambers are therefore sometimes configured to treat portions of asubstrate surface by turns. An exemplary thermal processing apparatus,such as the DSA® chamber available from Applied Materials, Inc., ofSanta Clara, Calif., may be used to irradiate a small portion of thesubstrate surface with laser light to anneal the surface. At the edge ofthe laser beam, the substrate surface may be heated at an extreme rate,and the temperature gradient between the irradiated portion and theuntreated portion may cause damaging thermal stress within thesubstrate. For this reason, the substrate is generally disposed on aheated chuck that maintains the entire substrate at an elevated ambienttemperature to reduce the stress of heating to the anneal temperature.Frequently, however, the requirement of maintaining the substrate at anelevated temperature reduces the benefit of the thermal treatment.Embodiments of the current invention generally contemplate improved waysof thermally treating the substrate.

In general the term “substrates” as used herein can refer to articlesformed from any material that has some natural electrical conductingability or a material that can be modified to provide the ability toconduct electricity. Typical substrate materials include, but are notlimited to, semiconductors, such as silicon (Si) and germanium (Ge), aswell as other compounds that exhibit semiconducting properties. Suchsemiconductor compounds generally include group III-V and group II-VIcompounds. Representative group III-V semiconductor compounds include,but are not limited to, gallium arsenide (GaAs), gallium phosphide(GaP), and gallium nitride (GaN). Generally, the term “semiconductorsubstrates” includes bulk semiconductor substrates as well as substrateshaving deposited layers disposed thereon. To this end, the depositedlayers in some semiconductor substrates processed by the methods of thepresent invention are formed by either homoepitaxial (e.g., silicon onsilicon) or heteroepitaxial (e.g., GaAs on silicon) growth. For example,the methods of the present invention may be used with gallium arsenideand gallium nitride substrates formed by heteroepitaxial methods.Similarly, the invented methods can also be applied to form integrateddevices, such as thin-film transistors (TFTs), on relatively thincrystalline silicon layers formed on insulating substrates (e.g.,silicon-on-insulator [SOI] substrates).

Some embodiments of the invention provide methods of thermally treatinga substrate. FIG. 1A is a schematic isometric view an apparatus 100according to one embodiment of the invention. FIG. 1A features an energysource 102 adapted to project an amount of energy on a defined region,or a anneal region 104, of a substrate 106 disposed on a work surface108. The amount of energy projected onto the anneal region 104 isselected to cause annealing of the surface of the substrate 106. In someembodiments, the energy delivered by the energy source is less than thatrequired to melt a portion of the substrate 106. In other embodiments,the energy delivered is selected to cause preferential melting of aportion of the substrate 106.

In some embodiments, the energy source 102 comprises a plurality ofemitters, as illustrated schematically in FIG. 1B, wherein emitters102A-102E are shown embedded in energy source 102. The emitters102A-102E generally emit radiation that is directed onto the substrate106. In some embodiments, each of the emitters 102A-102E emits the sameamount of energy. In other embodiments, the emitters 102A-102E may emitdifferent amounts of energy. In one exemplary embodiment, the emitter102A may emit an amount of energy selected to anneal the anneal region104 of the substrate 106, while the emitters 102B-102E emit an amount ofenergy selected to preheat one or more portions of the substrate 106near, adjacent to, or overlapping with the anneal region 104.

In one example, as shown in FIG. 1A, only one defined region of thesubstrate, such as anneal region 104, is exposed to the radiation fromthe energy source 102 at any given time. In one aspect of the invention,multiple areas of the substrate 106 are sequentially exposed to adesired amount of energy delivered from the energy source 102 to causepreferential melting of desired regions of the substrate. In anotheraspect, multiple areas of the substrate 106 are sequentially exposed toan amount of energy from the energy source 102 selected to annealdesired regions of the substrate without melting.

In general, the areas on the surface of the substrate may besequentially exposed by translating the substrate relative to the outputof the electromagnetic radiation source (e.g., conventional X/Y stage,precision stages) and/or translating the output of the radiation sourcerelative to the substrate. Typically, one or more conventionalelectrical actuators 110 (e.g., linear DC servo motor, lead screw andservo motor), which may be part of a separate precision stage (notshown), are used to control the movement and position of substrate 106.Conventional precision stages that may be used to support and positionthe substrate 106 are available from Parker Hannifin Corporation, ofRohnert Park, Calif.

In other embodiments, the source of electromagnetic radiation may betranslated relative to the substrate. In the embodiment of FIG. 1A, forexample, the energy source 102 may be coupled to a positioning apparatus(not shown), such as a Cartesian frame, adapted to position the energysource 102 over the desired region of the substrate 106. The positioningapparatus may additionally be configured to adjust elevation of theenergy source above the substrate 106.

Referring again to FIG. 1A, a preheat region 112 is defined on thesurface of the substrate 106. In some embodiments, the preheat region112 surrounds the anneal region 104. In other embodiments, the preheatregion may be adjacent to the anneal region 104, or may overlap with theanneal region 104. In still other embodiments, the preheat region 112may be near the anneal region 104, with a gap or space between thepreheat region 112 and the anneal region 104. In some embodiments, thepreheat region may be spaced apart from the anneal region. The preheatregion may thus have any convenient shape, such as the circular preheatregion 112 shown in the embodiment of FIG. 1A.

FIG. 2 is a schematic isometric view of an apparatus 200 according toanother embodiment of the invention. An energy source 202 is configuredto direct energy toward a substrate 204 disposed on a work surface 206.In some embodiments, the energy source 202 comprises a plurality ofemitters 202A that emit electromagnetic energy of a nature selected tothermally treat a surface of the substrate 204. At least one of theemitters 202A may be adapted to anneal an anneal portion 208 of thesubstrate 204, while at least one of the emitters 202A is adapted topreheat a preheat portion 210 of the substrate 204. In the embodiment ofFIG. 2, the preheat portion 210 is shown adjacent to the anneal portion208. Other embodiments may feature a preheat portion 210 that overlapsthe anneal portion 208, or is spaced apart from the anneal portion 208.

FIG. 3A is a generalized graph showing the effect on a substrate ofimplementing an embodiment of the invention. As shown in FIG. 3A,portions of the substrate are maintained at different temperatures indifferent zones. The graph of FIG. 3A schematically represents thetemperature of points on the surface of a substrate undergoing an annealprocess, the points arranged on a line drawn through the treatment zone.A first zone 302 may be maintained at a high temperature selected toanneal the substrate surface. This zone may correspond to the annealregion 104 of FIG. 1A, the anneal region 204 of FIG. 2, or any region ofa substrate to be heated to a high temperature.

The embodiment of FIG. 3A features a second zone 304 generallymaintained at a different temperature, which is lower in the example ofFIG. 3A. The second zone 304 may surround the first zone 302 in someembodiments. In other embodiments, the second zone 304 may be adjacentto the first zone 302, may overlap the first zone 302, or may be spacedapart from the first zone 302. The temperature of the second zone 304 isgenerally lower than that of the first zone 302. The temperature of thesecond zone 304 may be selected to preheat portions of the substrate,reducing the thermal stress on the substrate due to very abrupttemperature changes.

A third zone 306 is generally also defined on the substrate. In mostembodiments, the third zone 306 will be a zone in which ambienttemperature predominates. The third zone 306 may thus be an ambient zonein many embodiments. In some embodiments, however, the third zone 306may also receive applied thermal energy, either by ambient heating with,for example, a heated support, or by further use of electromagneticenergy. The temperature of the third zone 306 will generally be lessthan that of the second zone 304, following the idea of progressivepreheating closer to the first zone 302. The third zone 306 may surroundthe second zone 304 in some embodiments, or may be adjacent to thesecond zone in other embodiments. In some embodiments, the temperatureof the third zone will be maintained below about 500° C.

The second zone 304 may have a temperature between that of the firstzone 302 and the third zone 306. To accomplish the desired preheating,the temperature of the second zone 304 may effect a temperature rise ofbetween about 30% and about 70% of the full temperature rise from thetemperature of the third zone 306 to that of the first zone 302. In someembodiments, the temperature rise of the second zone 304 relative to thethird zone 306 is about 50% of the temperature rise of the first zone302 relative to the third zone 306.

In some embodiments, the temperature of the first zone 302 may bebetween about 1,100° C. and about 1,400° C., such as between about1,250° C. and about 1,350° C. In some embodiments, the temperaturedifference between the first zone 302 and an ambient temperature will bebetween about 90% and about 99%, such as about 95%, of the temperaturedifference between the melting point of the substrate and the ambienttemperature. In some embodiments, the temperature of the second zone 304may be between about 300° C. and about 800° C. The temperature of thesecond zone 304 is generally selected to diminish thermal stress at theboundary between the first zone 302 and the second zone 304, but is alsogenerally below the level at which portions of the substrate areamorphized. The temperature of the second zone 304 will generally beselected to preheat portions of the substrate to be annealed whilecooling portions that have been annealed. The temperature of the secondzone 304 is generally below that required to dislodge atoms from thecrystal lattice. In one exemplary embodiment featuring asilicon-containing substrate, the temperature of the first zone 302 maybe about 1,350° C., that of the second zone 304 about 650° C., and thatof the third zone 306 about 20° C., or another ambient temperature.

FIGS. 3B and 3C are schematic diagrams of substrates, each having aplurality of treatment zones defined thereon. The treatment zonesrepresent areas of the substrate being heated by electromagneticradiation. The embodiment of FIG. 3B has a first zone 302B surrounded bya second zone 304B and a third zone 306B. It should be noted that thezones may have similar or different shapes. The embodiment of FIG. 3Bfeatures a rectangular first zone 302B, with circular second and thirdzones 304B and 306B. Alternate embodiments may have circular shapes forall three zones. The embodiment of FIG. 3C features a rectangular firstzone 302C, with a rectangular or square second zone 304C adjacent to thefirst zone 302C on either side, all surrounded by a third zone 306C,which is an ambient zone. It should also be noted that the second zonemay be maintained at a single temperature throughout, or portions of thesecond zone may be maintained at different temperatures. For example,the second zone 304B of the embodiment of FIG. 3B may be a singletemperature throughout, whereas the second zone 304C of the embodimentof FIG. 3C may have portions at different temperatures. If one portionof the second zone 304C is intended as a preheat zone and another as acool-down zone, the preheat portion may be maintained at a highertemperature than the cool-down portion. It should be noted that asubstrate of any reasonable shape, such as circular, rectangular, or anyother planar shape, will benefit from embodiments of the inventiondescribed herein.

In some embodiments, there may be multiple zones of elevated temperaturebetween the ambient zone and the anneal zone. Some embodiments mayfeature a plurality of preheat zones with a single anneal zone. Someembodiments may feature a first plurality of preheat zones and a secondplurality of cool-down zones. In some embodiments, one zone may surroundthe zone of next higher temperature, such that each zone surrounds, andis surrounded by, another zone. Such embodiments may have zones thatapproximate concentric circles in shape, or nested circles with centersat different points (i.e. non-concentric circles). Zones of manydifferent shapes may be useful in some embodiments, such as variousdifferent polygonal shapes, for example triangular, rectangular, square,trapezoidal, hexagonal, and the like. Naturally, different shapes may beused for different zones. In other embodiments, a zone may be adjacentto the zone of next higher temperature on one side and next lowertemperature on the other side. In still other embodiments, some zonesmay be adjacent to other zones, and some zones may surround other zones.For example, a first zone may be defined as an anneal zone, with anadjacent second zone for preheat on a first side of the first zone andcool-down on a second side of the first zone, with both the first andsecond zones surrounded by a third zone, which is maintained at atemperature above ambient temperature, and a fourth zone surrounding allthe other zones maintained at ambient temperature.

In one exemplary embodiment, a rectangular anneal zone may be surroundedby one or more preheat zones shaped like a rectangle with triangles onopposite sides. Such a tapered shape may facilitate heating and coolingof the substrate surface in a desirable way. In another exemplaryembodiment, an anneal zone that may be rectangular or circular may besurrounded by one or more preheat zones having a teardrop shape. Therounded portion of the teardrop shape may be a preheat zone, while the“tail” of the teardrop may be a cool-down zone.

In some embodiments, one or more of the preheat or cool-down zones maybe spaced apart from the anneal zone, with a gap between the anneal zoneand the preheat and/or cool-down zones. For example, four zones may bedefined on a substrate surface to be annealed, an ambient zone, apreheat zone, an anneal zone, and a cool-down zone. The anneal zone maybe a rectangle having two long sides measuring 11 mm and two short sidesmeasuring 100 μm. The preheat zone may be an isosceles triangle with abase measuring 13 mm and height of 5 mm, with the base parallel to along side of the anneal zone, spaced about 1 mm from the long side ofthe anneal zone, and centered with respect to the anneal zone such thata line that bisects the isosceles triangle also bisects the anneal zoneinto two rectangles 5.5 mm long and 100 μm wide. The cool-down zone maylikewise be an isosceles triangle similar to the preheat zone. If theanneal zone temperature is 1,200° C., the temperature of the preheatzone may be between about 600° C. and about 700° C., such that thetemperature of the substrate surface falls slightly as it passes throughthe gap between the preheat zone and the anneal zone. The temperature ofthe substrate surface may, for example, fall to about 500° C. prior topassing into the anneal zone. Such a preheat profile may be useful forminimizing perturbation of atoms deep in the bulk of the substrate whilepreheating the surface. Extending the length of the base of theisosceles triangle that forms the preheat zone may provide heating forareas of the substrate surface adjacent to the short side of the annealzone to prevent damaging thermal stresses on the substrate. A similarcool-down zone located adjacent the opposite long side of the annealzone from the preheat zone may be useful for accelerating cooling whileavoiding damaging thermal stresses.

Some embodiments may feature a plurality of anneal zones and a pluralityof zones having different intermediate temperatures. Each anneal zonemay be maintained at the same temperature, or at different temperaturesdepending on the needs of individual embodiments. In embodiments of thissort, preheat zones may be defined between, among, around, adjacent to,surrounding, or spaced apart from anneal zones. For example, in oneembodiment, a substrate may be processed in four portions by anapparatus that defines a plurality of treatment zones in each portion.Thus, each portion may have an anneal zone surrounded by a preheat zone,and further by an ambient zone, the zones translating across eachportion simultaneously to process the substrate. In such an embodiment,the zones may be shaped and configured in any of the ways describedelsewhere herein, and the position of the heated zones within eachportion may be maintained at a pre-selected distance from the heatedzones within the other portions to manage the overall thermal budget ofthe substrate.

In some embodiments, the preheat zones, or the preheat and cool-downzones, may be shaped in a convenient way. Embodiments have beendescribed in which the preheat and cool-down zones are rectangular, andare disposed on two sides of an anneal zone, as depicted in theembodiment of FIG. 3C. In other embodiments, the shape of the preheatand cool-down zones may be tapered away from the anneal zone. Inembodiments wherein the preheat and cool-down zones do not surround theanneal zone, the preheat and cool-down zones will generally becoextensive with at least one dimension of the anneal zone. In someembodiments, the preheat and cool-down zones may grow narrower withdistance from the anneal zone. In some embodiments, the preheat andcool-down zones may have triangular, trapezoidal, parabolic, elliptical,oval, or irregular shapes. In other embodiments, the preheat andcool-down zones may have the shape of a rectangle coupled to asemi-circle. The shapes may be mixed, with a preheat zone having oneshape and a cool-down zone having another shape. In embodiments whereinthe preheat and cool-down zones surround the anneal zone to form asingle intermediate-temperature zone, the singleintermediate-temperature zone may be shaped as well. Anintermediate-temperature zone surrounding an anneal zone may have anelliptical, oval, or diamond shape in some embodiments. In otherembodiments, a rectangular zone may surround the anneal zone. In stillother embodiments, the intermediate-temperature zone may have irregularor complex-regular shape, such as a pair of abutting trapezoids.

In one embodiment, the intermediate-temperature zone may have agenerally oval shape and may be irregularly placed with respect to theanneal zone. In such an embodiment, a centroid of the anneal zone willbe displaced away from a centroid of the intermediate-temperature zone.Thus, a plurality of line segments drawn from starting points on theedge of the intermediate-temperature zone, each segment perpendicularthereto at its respective starting point, to ending points on the edgeof the anneal zone will have lengths ranging from a maximum to a minimumvalue. It may be advantageous to maintain more distance between the edgeof the anneal zone and the edge of the intermediate-temperature zone inthe direction of the anneal path, so that as the anneal energy movesacross the surface of the substrate, enough preheat energy is applied toprevent damage to the substrate, and enough energy is applied to thecool-down zone to facilitate rapid cooling without damage afterannealing is finished. In such an embodiment, a plot of temperatureversus time for a particular point on the substrate surface may have theshape of half a teardrop.

FIG. 4 is a schematic side view of an apparatus 400 according to anotherembodiment of the invention. A first energy source 402 and a secondenergy source 404 are disposed to direct energy toward a first surface406, and a second surface 408, respectively, of a substrate 410. Thefirst energy source 402 directs energy toward a first zone 412 of thesubstrate 410. The second energy source 404 directs energy toward asecond zone 414 of the substrate 410. In most embodiments, the firstzone 412 is smaller than the second zone 414, and the boundaries of thesecond zone 414 extend beyond the boundaries of the first zone 412 onall sides. In most embodiments, the first energy source 402 directselectromagnetic energy toward the substrate 410, irradiating the firstzone 412 with energy selected to heat the first zone 412 to an annealtemperature, while the second energy source 404 irradiates the secondzone 414 with energy selected to heat the second zone 414 to anintermediate temperature. The heating of the second zone 414 to anintermediate temperature serves to preheat portions of the substrate tobe annealed to avoid severe thermal stresses due to abrupt temperaturechanges at the edges of the first zone 412. In general, an energy sourcedesigned to anneal a substrate will deliver power density of at least 1W/cm² to the substrate surface, and an energy source designed to merelyheat the substrate will deliver power density of at least 0.1 W/cm², butless than that required to anneal.

In one aspect, the anneal region is sized to match the size of anindividual die (e.g., 40 “dice” are shown in FIG. 1A), or semiconductordevice (e.g., memory chip), formed on the surface of the substrate.Referring again to FIG. 1A, in one aspect, the boundary of the annealregion 104 is aligned and sized to fit within “kerf” or “scribe” lines114 that define the boundary of each die. In one embodiment, prior toperforming the annealing process the substrate is aligned to the outputof the energy source 102 using alignment marks typically found on thesurface of the substrate and other conventional techniques so that theanneal region 104 can be adequately aligned to the die. Sequentiallyplacing anneal regions 104 so that they only overlap in the naturallyoccurring unused space/boundaries between dice, such as the scribe orkerf lines 114, reduces the need to overlap the energy in the areaswhere the devices are formed on the substrate and thus reduces thevariation in the process results between the overlapping anneal regions.This technique has advantages over conventional processes that sweep thelaser energy across the surface of the substrate, since the need totightly control the overlap between adjacently scanned regions to assureuniform annealing across the desired regions of the substrate is not anissue due to the confinement of the overlap to the unused space betweendice. Confining the overlap to the unused space/boundary between dicealso improves process uniformity results versus conventional scanninganneal type methods that utilize adjacent overlapping regions thattraverse all areas of the substrate. Therefore, the amount of processvariation, due to the varying amounts of exposure to the energydelivered from the energy source 102 to process critical regions of thesubstrate is minimized, since any overlap of delivered energy betweenthe sequentially placed anneal regions 104 can be minimized.

Referring to FIG. 1A, in one example, each of the sequentially placedanneal regions 104 is a rectangular region that is about 22 mm by about33 mm in size (e.g., area of 726 square millimeters (mm²)). In oneaspect, the area of each of the sequentially placed anneal regions 104formed on the surface of the substrate is between about 4 mm² (e.g., 2mm×2 mm) and about 1000 mm² (e.g., 25 mm×40 mm). A circular preheatregion 112 may surround the anneal region 104, and may extend up toabout 100 mm beyond an edge of the anneal region 104. In an embodimentsuch as that shown in FIG. 1A, the preheat region 112 will preferablyextend no less than about 50 mm beyond an edge of the anneal region 104.The extent of the preheat region or intermediate-temperature regionbeyond the anneal region will generally depend on the size of thesubstrate and the available energy delivery resources. It will bedesireable, in most embodiments, to size the various intermediatetemperature regions such that power requirements are minimized whileproviding the thermal budget management needed for the embodiment. Insome embodiments the intermediate-temperature region extends beyond theanneal region less than 100 mm in at least one direction, such as lessthan 50 mm, for example about 30 mm.

Referring now to FIG. 2, in another example, each anneal portion 208 mayhave dimensions similar to those of the anneal regions 104 of FIG. 1A.The preheat regions 210 are shown adjacent to the anneal portion 208 oneither side, and co-extensive with one dimension of the anneal portion208. The preheat regions 210 may extend between about 50 mm and about100 mm beyond the edge of the anneal portion 208 in some embodiments.

The size of the preheat zone or region will generally be selected toallow adequate preheating in the preheat zone. In some embodiments, eachpreheat zone may be larger than the anneal zone in order to allow foradequate preheating. In an embodiment featuring sequential exposure ofsuccessive anneal regions, the time required to preheat a preheat zoneto a desired temperature may be longer than the time required to annealthe anneal zone. Thus, an individual location on the substrate may besubjected to two or more preheat processes.

In most embodiments, the energy source is generally adapted to deliverelectromagnetic energy to anneal certain desired regions of thesubstrate surface. Typical sources of electromagnetic energy include,but are not limited to optical radiation sources (e.g., lasers),electron beam sources, ion beam sources, microwave energy sources,visible light sources, and infra-red sources. In one aspect, thesubstrate may be exposed to a pulse of energy from a laser that emitsradiation at one or more appropriate wavelengths for a desired period oftime. In another aspect, flash lamps may be used to generate visiblelight energy for pulsing onto the substrate. In one aspect, a pulse ofenergy from the energy source is tailored so that the amount of energydelivered to the anneal region and/or the amount of energy deliveredover the period of the pulse is optimized to perform targeted annealingof desired areas. In one aspect, the wavelength of a laser is tuned sothat a significant portion of the radiation is absorbed by a siliconlayer disposed on the substrate. For laser anneal processes performed ona silicon containing substrate, the wavelength of the radiation istypically less than about 800 nm, and can be delivered at deepultraviolet (UV), infrared (IR) or other desirable wavelengths. In oneembodiment, the energy source may be an intense light source, such as alaser, that is adapted to deliver radiation at a wavelength betweenabout 500 nm and about 11 micrometers. In most embodiments, the annealprocess generally takes place on a given region of the substrate for arelatively short time, such as on the order of about one second or less.

In some embodiments, the energy source comprises a plurality ofemitters, at least one of which emits annealing energy as describedabove, and at least one of which emits preheating energy. The preheatingenergy may be continuous wave energy or it may be delivered in pulses.The preheating energy may be coherent or incoherent, monochromatic orpolychrome, polarized or non-polarized, or any combination or degreethereof. The preheating energy may be delivered as intense white light,as infra-red light, or as laser light. Intense white light may bedelivered using xenon lamps. Infra-red light may be delivered using heatlamps. In some embodiments, the preheating energy may be delivered ascontinuous wave radiation, with the anneal energy delivered in pulses.The preheat energy is generally selected to raise the temperature of asubstrate a fraction of the amount required for annealing or melting. Inone embodiment, a laser may be disposed above a work surface, with fourheat lamps surrounding the laser to preheat an area around the annealzone. In another embodiment, four xenon lamps may be used to deliverintense white light instead of the heat lamps.

FIG. 5 is a schematic cross-sectional diagram illustrating a processingchamber 500 useful for practicing embodiments of the invention. Theprocessing chamber 500 comprises an optically transparent window 506formed on a chamber body 504. The chamber body 504 defines a processingvolume 502. In one embodiment, the processing volume 502 may have aninert environment maintained by an inert gas source 512 and a vacuumpump 510 connected to the processing volume 502.

A substrate support 508 is deposed in the processing volume 502. Thesubstrate support 508 is configured to support and move a substrate 514disposed on a top surface 516. An energy source 518 is positionedoutside the chamber body 504 and is configured to project energy throughthe optically transparent window 506. The energy source may beconfigured to project annealing energy 520 and preheat energy 522 in anyof the ways described elsewhere herein. The substrate support 508 may beconnected to a temperature control unit 524 having cooling and heatingcapacities for the substrate 514 disposed on the substrate support 508.The substrate support 508 may be connected to one or more high precisionstages 526 which allow precise alignment and relative movement betweenthe substrate 514 and the energy source 518 during processing.

In one embodiment, an optical sensor 528 may be used to assist alignmentof the substrate 514 with the energy source 518. The optical sensor 528may be positioned near the optically transparent window 506 andconnected to a control unit 530 which is further connected to the highprecision stage 526. During alignment, the optical sensor 528 may “look”through the optically transparent window 506 to locate visual markers onthe substrate 514, for example a notch, and a scribe line around a die.The control unit 530 processes signals from the optical sensor 528 andgenerates control signals to the high precision stage 526 for alignmentadjustment.

As described above, due to power requirements, a substrate is generallyannealed one portion at a time. After each individual anneal, theelectromagnetic energy must be translated with respect to the substrateto illuminate the next anneal portion. FIG. 6 is a schematic top view ofa substrate 600 that contains forty rectangular dice 602 arranged in anarray. Each die 602 is delimited by scribe lines 604, which also definean unused area 606 between the dice. A first energy projection region608 is provided to project a first quantity of energy toward a singledie 602. In general, the first energy projection region 608 may cover anarea equal to or greater than the area of each die 602, but smaller thanthe area of each die 602 plus the unused area 606 surrounding the scribelines 604, so that the energy delivered in the energy projection region608 completely covers the die 602 while not overlapping with theneighboring dice 602. A second energy projection region 610 is providedsurrounding the first energy projection region 608 to deliver a secondquantity of energy to the substrate 600. The first quantity of energywill generally differ from the second quantity of energy. In someembodiments, the first quantity of energy will have higher intensity andmore power than the second quantity of energy. In some embodiments, thefirst quantity of energy may be selected to anneal the portion of thesubstrate surface inside the first energy projection region 608. Inother embodiments, the first quantity of energy may be selected topreferentially melt portions of the substrate surface inside the firstenergy projection region 608. The second quantity of energy may beselected to preheat portions of the substrate surface in the secondenergy projection area 610. The preheat temperature rise of the secondenergy projection region 610 may be a fraction of that reached in thefirst energy projection region 608, such as between about 30% to about70%, or preferably about 50%. The second energy projection region 610thus maintains the temperature of the substrate surface therein belowthat reached in the first energy projection region 608, so that thetemperature gradient at the interface between the first and the secondenergy projection regions generates thermal stress in the substrate lessthan that required to damage the substrate.

To perform an annealing process on multiple dice 602 spread out acrossthe substrate surface, the substrate and/or the output of an energysource is positioned and aligned relative to each die 602. In oneembodiment, curve 612 illustrates a relative movement between the dice602 of the substrate 600 and the energy projection regions 608 and 610during an anneal sequence performed on each die 602 on the surface ofthe substrate 600. In one embodiment, the relative movement may beachieved by translating the substrate in x and y direction so that theyfollow the curve 612. In another embodiment, the relative movement maybe achieved by moving the energy projection regions 608 and 610 relativeto a stationary substrate 600. The energy projection regions 608 and 610may be moved by moving the energy source relative to the substrate 600,or by manipulating the energy itself. In an embodiment that useselectromagnetic energy, the energy may be manipulated using opticswithout moving either the substrate or the energy source. For example,one or more mirrors or lenses may direct the projected energy towardsuccessive dice 602, moving the energy projection regions 608 and 610accordingly.

Additionally, a path different than that represented by the curve 612may be used to optimize throughput and process quality depending on aparticular arrangement of dice 602. For example, an alternate annealpath may follow a substantially spiral pattern, starting with dice 602near the center of substrate 600 and proceeding in an expanding circularpattern, or starting with dice 602 at one edge of the substrate andproceeding in a contracting circular pattern. In one embodiment, it maybe advantageous to pursue an anneal path along diagonals, proceedingalong a path drawn through diagonals of dice 602. Such a path mayminimize the opportunity for overlap of anneal regions on successivedice 602.

As the energy source proceeds along an anneal path, the energyprojection regions move along the surface of the substrate. The secondenergy projection region 610 of FIG. 6 precedes the first energyprojection region 608 in all directions. The second energy projectionregion 610 may therefore be used to preheat portions of the substrate tobe annealed in the first energy projection region 608. Preheatingreduces the impact of thermal stresses on the substrate, preventingdamage to the substrate at the edge of the anneal region.

In an alternate embodiment, the second energy projection region may beadjacent to the first energy projection region. For example, the secondenergy projection region may be on both sides of the first energyprojection region extending outward in the direction of the anneal path.Thus, one part of the second energy projection region, the part thattravels in front of the first energy projection region as the projectedenergy travels along the anneal path, may preheat portions of thesubstrate to be annealed, while the other portion moderates cooling ofthe substrate behind the anneal region. An apparatus adapted to performan anneal process of this sort may advantageously have the capability torotate the energy sources when an extremity of the substrate is reached,so that the energy sources can travel in a different direction with thesecond energy projection region continuing ahead of the first energyprojection region.

In one embodiment, during an annealing process, the substrate 600 movesrelative to the energy projection regions 608 and 610, as shown by curve612 of FIG. 6. When a particular die 602 is positioned and alignedwithin the first energy projection region 608, the energy sourceprojects a pulse of energy towards the substrate 600 so that the die 602is exposed to a certain amount of energy over a defined durationaccording to the particular anneal process recipe. The duration of thepulsed energy is typically short enough so that the relative movementbetween the substrate 600 and the first energy projection region 608does not cause any “blur”, i.e. non uniform energy distribution, acrosseach die 602 and it will not cause damage to the substrate. Thus, theenergy projection regions 608 and 610 may move continuously with respectto the substrate 600, while short bursts of annealing energy impact thevarious dice 602 in the first energy projection region. Energy impactingthe second energy projection region 610 may likewise be pulsed orcontinuous. If pulsed, the energy projected toward the second energyprojection region will generally be of a nature selected to raise thetemperature of the substrate surface in the second energy projectionregion a substantial fraction, such as about 30% to about 70%, or morepreferably about 50%, of the temperature rise imparted to the firstenergy projection region over the exposure time of the first energyprojection region to manage the thermal budget of the substrate.

For example, if the first energy projection region experiences a firstpulse of incident energy that increases the temperature of the substratefrom 20° C. to 1,300° C., such as a 10 nanosecond laser burst, thesecond pulse of incident energy delivered to the second energyprojection region should raise the temperature of the substrate in thatregion to at least about 600° C. during the first burst. If necessary,the second pulse may be longer than the first pulse to allow the secondenergy projection region time to heat up. It may be advantageous, insome embodiments, for the second energy projection region to encompassthe first energy projection region, starting before the first pulse andending after the first pulse, such that a second pulse delivered over aninterval that encompasses the first pulse preheats the area to besubjected to the first pulse, along with adjacent areas of thesubstrate.

In other embodiments, the energy delivered to the second energyprojection region may be continuous, while that delivered to the firstenergy projection region is pulsed. In some embodiments, multiple pulsesof energy may be delivered to the first energy projection region, whilecontinuous energy is delivered to the second energy projection region.

FIG. 7 is a schematic cross-sectional view of an apparatus 700 accordingto another embodiment of the invention. The apparatus 700 comprises achamber 702 for processing a substrate 704. The substrate is positionedon a substrate support 706 inside the chamber 702. In the embodiment ofFIG. 7, the substrate support 706 is represented as a ring, because theembodiment of FIG. 7 irradiates the substrate 704 from the front sideand the back side. In alternate embodiments, the substrate 704 may beirradiated from one side only, and may rest on a substrate support suchas the exemplary substrate support 508 of FIG. 5. Lift pins 756, withactuators 758, raise and lower the substrate support 706 for insertionand removal of substrates from the chamber 702. The chamber 702 has alower portion 708 and an upper portion 710, that together define aprocessing volume 712. The upper portion generally has an upper wall 726that defines an upper processing volume 712A above the substrate 704.The upper portion 710 may have an opening 714 for depositing andretrieving substrates, and a gas inlet 716 to provide process gases froma process gas source 718. The upper portion 710 supports a first window720 made of a material selected for its light transmission andabsorption properties. A first energy source 722 is positioned outsidethe chamber 702 to direct a first energy 724 toward the first window720. The first window preferably admits some or all of the first energy724 into the chamber 702.

The lower portion 708 of the chamber 702 comprises a lower chamber wall728 that defines a lower processing volume 712B. The lower portion 708may have a gas outlet 730 coupled to a pump 732 for removing processgases from the chamber 702. The lower portion 708 of the chamber 702houses a second energy source 734. The second energy source 734comprises a plurality of light sources 736 for generating a secondenergy 738 and directing the second energy 738 toward the substrate 704.A second window 740 covers the plurality of light sources 736. Eachlight source is housed in a tube 746, which may be reflective to directenergy from the light source 736 toward the substrate 704. The lightsources 736 are generally powered by a power supply 742. In theembodiment of FIG. 7, power from the power supply 742 is routed througha switching box 744 that routes power from the power supply 742 to oneor more of the light sources 736. By controlling the operation of theswitching box 744, the light sources 736 can be selectively energized.

In many embodiments, the light sources 736 will be infra-red lightgenerators, such as heat lamps, but they may also be configured togenerate broad-spectrum light, ultra-violet light, or combinations ofwavelengths across the broad spectrum from ultra-violet to infra-red. Insome embodiments, the light sources 736 may be white light lamps, suchas halogen lamps, or flash lamps. The second energy 738 generated by thelight sources 736 heats a portion of the substrate 704 to an elevatedtemperature that is not sufficient to anneal the substrate. Thus, thelight sources 736 serve as preheat energy sources. The portion of thesubstrate 704 treated by the second energy 738 is therefore a preheatzone 746.

In many embodiments, the first energy source 722 may be a laser capableof generating light at wavelengths readily absorbed by the substrate704. In other embodiments, the first energy source 722 may be a flashlamp or white light source. The first energy 724 generated by the firstenergy source 722 heats a portion of the substrate 704 to an elevatedtemperature sufficient to anneal the portion of the substrate 704. Thus,the first energy source 722 serves as an anneal energy source. Theportion of the substrate 704 treated by the first energy 724 istherefore an anneal zone 748.

As described above, the substrate 704 is preferably treated in portions.An actuator 750 is provided to position the first energy source 722 overan anneal region 748. A controller 752 operates the actuator 750 toposition the first energy source 722 over the anneal zone 748 andoperates the switching box 744 to switch power to one or more lightsources 736 to direct preheat energy toward the preheat zone 746. Inthis way, a portion of the substrate is preheated before annealing. Thecontroller 752 operates to move the preheat zone 746 and the anneal zone748 together so that any portion of the substrate 704 that is annealedis first preheated, but most of the substrate 704 remains at an ambienttemperature, defining an ambient zone 754.

FIGS. 8A and 8B are graphs showing temperature-time profiles for twoembodiments of the invention. Each graph shows the temperature of onepoint on the surface of a substrate undergoing thermal processingaccording to embodiments of the invention. As described above, thesubstrate moves relative to the energy sources directing energy towardthe substrate surface. In FIG. 8A, as the exemplary point on thesubstrate surface moves from an ambient zone to a first preheat zone,the temperature of that point moves from an ambient temperature in anambient temperature interval 800 to a first preheat temperature in afirst preheat interval 802. As described elsewhere herein, the firstpreheat temperature is generally lower than that required to anneal thesubstrate surface. As the exemplary point moves from the first preheatzone to a second preheat zone, the temperature of that point moves fromthe first preheat temperature in the first preheat interval 802 to asecond preheat temperature in a second preheat interval 804. Theembodiment of FIG. 8A illustrates four zones defined on the substratesurface, an ambient zone, two preheat zones, and an anneal zone. As theexemplary point on the substrate surface moves from the second preheatzone to an anneal zone, the temperature of that point moves from thesecond preheat temperature in the second preheat interval 804 to ananneal temperature in an anneal interval 806. As the exemplary pointmoves out of the anneal zone back into lower temperature zones, itexperiences cooling to the conditions of the second preheat interval 804in a first cool-down interval 808, to the conditions of the firstpreheat interval 802 in a second cool-down interval 810, and finally toambient conditions in a second ambient interval 812. It should be notedthat alternate embodiments may feature temperatures during the cool-downintervals 808 and 810 that are different from those in the preheatintervals 802 and 804. Thus, the temperature in cool-down interval 808may be higher or lower than the temperature in preheat interval 802, andthe temperature in cool-down interval 810 may be higher or lower thanthe temperature in preheat interval 804. It should be understood thatsimilar embodiments may feature only one preheat interval or more thantwo preheat intervals. Likewise, some embodiments may feature only onecool-down interval or more than two cool-down intervals.

The graph of FIG. 8B describes the temperature-time profile of one pointon a substrate surface undergoing thermal processing according toanother embodiment of the invention. In the embodiment of FIG. 8B, theexemplary point on the substrate surface moves from an ambient interval850 to a first preheat interval 852, similar to the embodiment of FIG.8A. The exemplary point then moves into a second preheat interval 854that features a varying temperature-time profile. In this embodiment, asthe exemplary point moves through the second preheat interval 854, thetemperature at that point rises from a first preheat temperature to asecond preheat temperature. The rise may be linear as shown in interval854, or it may have some other profile, even including short intervalsof decreasing temperature within the generally rising temperature-timeprofile of the second preheat interval 854. The exemplary point movesinto the anneal interval 856, and then into the first cool-down interval858, which may also have a varying temperature-time profile, much likethat of the second preheat interval 854. The exemplary point then movesinto the second cool-down interval 860, followed by the second ambientinterval 862.

FIG. 9 is a flow diagram showing a method 900 according to oneembodiment of the invention. At 910, a substrate is provided to athermal treatment chamber. At 920, a plurality of zones is defined on asurface of the substrate. Each zone is treated using electromagneticenergy with different levels of power. In most embodiments, there willbe at least three zones, but embodiments of the invention arecontemplated featuring two zones or more than three zones. In mostembodiments, at least one zone will be an anneal zone, treated withelectromagnetic energy selected to anneal the surface of the substrate.In some embodiments, it may be desirable to melt the substrate surfacein the at least one anneal zone. In most embodiments, at least one zonewill be a preheat zone. In some embodiments, one or more zones may becombined preheat and cool-down zones, whereas in other embodiments oneor more zones may be exclusively preheat or cool-down zones.

In one aspect, a substrate is disposed on a substrate support, and afirst quantity of electromagnetic energy is directed toward a firstportion of the substrate. Additionally, a second quantity ofelectromagnetic energy is directed toward a second portion of thesubstrate, wherein the first portion of the substrate surrounds thesecond portion of the substrate, the first quantity of electromagneticenergy preheats the first portion of the substrate, and the secondquantity of electromagnetic energy anneals the second portion of thesubstrate. The first quantity and second quantity are moved across thesubstrate, maintaining a constant spatial relationship between the twoquanta of energy, such that the area of the substrate within the firstand second portions moves as the energy moves.

In another aspect, the electromagnetic energy delivered in the twoquanta may be of any desired nature. The energy of each quantity may becoherent or incoherent, monochromatic or polychromatic, polarized orunpolarized, and continuous or pulsed to any degree. The energy of eachquantity may be delivered by one or more lasers, intense white lightlamps, flash lamps, heat lamps, or combinations thereof. The two quantaof energy may be delivered by electromagnetic energy differing only inintensity, or the two quanta may differ by any desired degree in any ofthe characteristics mentioned above. In one example, the first quantitymay be delivered by one or more lasers, each delivering at least 100W/cm² of power at a wavelength less than about 850 nm. The lasers may bepulsed or continuous wave energy sources. In pulsed embodiments, thepulsing may be realized by cycling power to the lasers or by virtue ofoptical switching that intermittently blocks the laser light fromleaving the optical assembly. In another example, the second quantitymay be delivered by one or more lamps delivering incoherent light to thesecond portion at a power level of less than 50 W/cm², such as about 25W/cm².

FIG. 10 is a flow diagram summarizing a method 1000 according to anotherembodiment of the invention. At 1010 a substrate is positioned on asubstrate support in a thermal treatment chamber. At 1020, a firstsource of electromagnetic energy is directed toward a first portion ofthe substrate. At 1030, a second source of electromagnetic energy issimultaneously directed toward a second portion of the substrate. Asdescribed elsewhere herein, one of the sources may be configured todeliver annealing energy while the other is configured to deliverpreheat energy. At 1040, the substrate is translated with respect to thefirst and second energy sources. Translating the substrate causes thedelivered energy to translate across the substrate surface to anneal theentire surface in portions. In the embodiment of FIG. 10, the energysources are substantially stationary, while the substrate moves, butcertain embodiments may feature movement of the energy sources, or theenergy, in addition to movement of the substrate. Translation of thesubstrate is generally accomplished by using a moveable substratesupport, such as a precision stage capable of positioning the substrateat a precise location within the apparatus.

In most embodiments, the zones are maintained at different temperatures.In some embodiments, the zones are heated by directing electromagneticenergy of various types and intensities toward the substrate surface. Inthe embodiment of FIG. 9, each zone is irradiated using electromagneticenergy of a different power level at 930. In other embodiments,additional heat may be imparted to the substrate by use of a heatedsubstrate support contacting the back side of the substrate. In stillother embodiments, portions of the substrate may be selectively cooledby a cooled substrate support contacting the back side of the substrate.The temperature in at least one of the zones will be selected to annealthe surface of the substrate. The temperature in a least one of thezones will be selected to preheat the surface of the substrate, and willbe lower than that required to anneal the substrate surface. One zone,which may be an anneal zone, will receive the maximum power level. Otherzones will receive lesser power levels. One or more zones, which may bepreheat zones, may receive elevated power levels below that of themaximum level. Still other zones may receive negligible power, or may becooled. Some zones may be ambient zones, wherein the temperature of thesubstrate is maintained at ambient temperature.

In some embodiments, the different zones may be irradiated usingdifferent sources of electromagnetic energy. One or more lasers mayprovide the electromagnetic energy. A first laser may generate energy toanneal a portion of the substrate in one zone, and a second laser maygenereate energy to preheat a portion of the substrate in another zone.In an alternate embodiment, a plurality of lasers may preheat portionsof the substrate. In another embodiment, for example the embodiment ofFIG. 7, one or more heat lamps may preheat portions of the substrate.

In embodiments wherein a plurality of zones includes an anneal zone, thezones providing preheat or cool-down functions may be shaped tofacilitate preheat or cool-down. In an exemplary embodiment with ananneal zone having a preheat zone on one side and a cool-down zone on anopposite side, the preheat zone and the cool-down zone may have atapered shape, with a first edge abutting an edge of the anneal zone andcoextensive with the edge of the anneal zone, and a second edge oppositethe first edge and shorter than the first edge forming a trapezoidalshape. In alternate embodiments, the preheat and cool-down zones may betriangular in shape, with one edge of each coextensive with an edge ofthe anneal zone. In other alternate embodiments, the tapered extremityof the preheat and cool-down zones may be curved, and may be parabolicor semi-circular in some embodiments.

The plurality of zones having different temperatures and shapesgenerally allows for rapid annealing of the substrate by exposingportions of the substrate surface to electromagnetic energy designed toexcite movement of atoms in the substrate lattice, while keeping thermalstresses below a threshold level which, if passed, would damage thesubstrate. The preheat and cool-down zones allow the anneal treatment tocommence from an elevated temperature, speeding the ultimate temperatureramp-up and cool-down during annealing. The tapered shape of the preheatand cool-down zones may serve to minimize thermal exposure of portionsof the substrate not being annealed, which minimizes unwanted movementof atoms that may have been repositioned by the anneal process, or atomsthat may have been in desireable positions before the anneal process. Ingeneral, the number and shape of preheat and cool-down zones may beselected to facilitate the desired anneal process.

The embodiments described above generally feature zones havingsubstantially constant temperature. A first zone is maintained at afirst temperature, a second zone at a second temperature, and so forth.In other embodiments, one or more zones may have a temperature gradientto facilitate heating or cooling near the anneal zone. In a three-zoneembodiment, for example, a first zone, which may be a preheat zone, mayhave a temperature gradient that increases toward a second zone, whichmay be an anneal zone. Likewise, a third zone, which may be a cool-downzone, may have a temperature gradient that increases toward the secondzone. The temperature gradient provides the same general function as thetapered zone shape described above. A temperature gradient may beestablished within a given zone by use of optics to adjust the deliveredenergy to achieve a desired temperature profile.

In one exemplary embodiment, a single energy source of sufficient powerto anneal a substrate may be oriented to direct electromagnetic energytoward the substrate. A lens having defocusing characteristics may bedisposed between the energy source and the substrate. The lens may havea first portion that defocuses a corresponding first portion of theelectromagnetic energy, and a second portion that either focuses asecond portion of the electromagnetic energy further or leaves itunchanged. For example, if a laser is used as the source ofelectromagnetic energy, and shaping optics are used to form a circularannealing energy beam 2 mm in diameter, a lens may be disposed betweenthe shaping optics and the substrate that has a circular central portionwith radius 0.5 mm surrounded by a concentric annular outer portion withradius 1.5 mm. The circular central portion may have neutral optics, ifdesired, or may focus the portion of the annealing energy beam incidenton that portion. The concentric annular outer portion of the lens may beshaped to reduce the intensity of the outer portion of the annealingenergy beam. The reduced intensity energy will then impinge upon thesurface of the substrate with enough power to preheat a preheat portionof the surface without annealing it, while the unchanged or focusedportion anneals an anneal portion within the preheat portion.

FIG. 11 is a flow diagram summarizing a method 1100 according to anotherembodiment of the invention. A substrate is positioned on a substratesupport in a thermal treatment chamber at 1102. A plurality of zones isdefined on the substrate surface at 1104. A first portion of the zonesis maintained at an ambient temperature at 1106. The ambient temperaturemay be room temperature in some embodiments, or it may be an elevatedtemperature in other embodiments. In most embodiments, the ambienttemperature will be less than about 200° C., but some embodiments mayfeature an ambient temperature as high as 350° C. The ambienttemperature may be maintained by use of a heated substrate support, orby irradiating the substrate with electromagnetic energy suitable forthe desired heating.

At 1108, preheat energy is provided to a second portion of the definedzones to heat them to one or more intermediate temperatures higher thanthe ambient temperature. Each zone may be heated to the sameintermediate temperature, or to a different intermediate temperature.Zones closer to the area to be annealed will generally be maintained ata temperature that is the same as, or higher than, that of zones furtherfrom the area to be annealed. In embodiments wherein the second portioncomprises more than one zone, the intermediate temperatures may rise ina stepwise fashion from the ambient temperature to an annealtemperature. The temperature difference between an intermediatetemperature and the ambient temperature will generally be between about10% and about 90% of the temperature difference between the annealtemperature and the ambient temperature, such as between about 30% andabout 70%, for example about 50%. In an exemplary embodiment wherein thesecond portion comprises two zones, the temperature difference betweenthe first intermediate temperature zone and the ambient zone may beabout 40% of the temperature difference between the anneal temperatureand the ambient temperature, while the difference between the secondintermediate temperature zone and the ambient zone is about 60% of thedifference between the anneal temperature and the ambient temperature.

At 1110, annealing energy is provided to a third portion of the definedzones to heat them to one or more anneal temperatures higher than theambient and intermediate temperatures, and selected to anneal thesubstrate surface. The anneal zones, comprising the third portion ofdefined zones, may have any of the spatial relationships describedherein. Additionally, different anneal temperatures may be applied todifferent anneal zones, if desired.

At 1112, one or more of the foregoing temperatures may be detected andused to control delivery of the preheat energy, the anneal energy, orboth to keep thermal gradients between the zones below a thresholdlevel. In some embodiments, one or more thermal imaging devices may beused to detect the temperature of various zones. The temperature of onezone may be compared to the temperature of another zone to determinewhether the thermal gradients between the zones are excessive. Theenergy delivered to one or more of the detected zones may be modulatedbased on the detected temperatures to increase or reduce the thermalgradient between those two zones. If the substrate is annealed by movingthe energy sources, the detector may be co-located with the energysources to follow the anneal and preheat zones around the substrate. Ifthe substrate is annealed by moving only the energy (e.g. usingmirrors), similar optics may be used to focus the detector on theportion of the substrate being treated, under the direction of acontroller, or the entire substrate may be sampled and a computer usedto determine the thermal gradients of interest.

Examples

In one exemplary embodiment, a substrate may be positioned on a supportin a thermal processing apparatus. The substrate may be held in place onthe support by any means known to the art, including electrostatic orvacuum means. A laser is disposed above the substrate and oriented suchthat it produces a beam of light that impinges the substrate in adirection substantially perpendicular to the plane of the substrate. Thelaser may be coupled to an optical assembly adapted to position thelaser in three dimensions. The laser may be adapted to deliver laserenergy of up to 10 kW/cm² to an anneal region of the substrate measuring22 mm by 33 mm. The laser is preferably tuned to a wavelength readilyabsorbed by the substrate, such as less than 800 nm for a siliconsubstrate.

In operation, the laser may be switched using an electrical switchcoupled to the power supply or an optical switch coupled to the laser orthe optical assembly. The switches may be configured to switch the laseron or off in less than 1 microsecond (psec), such that the laser candeliver pulses of energy lasting from about 1 psec to about 10milliseconds (msec).

For this example, a preheat light source is co-located with the laser inthe optical assembly. The preheat light source may be another laser, axenon lamp, or a heat lamp, and may be adapted to deliver up to 500 W ofelectromagnetic energy to a substantially circular area encompassing,and concentric with, the anneal area, and measuring about 2 cm indiameter. The preheat light source may be focused using appropriatelenses and mirrors to capture and direct all the energy of the preheatlight source. The preheat light source may be located in a housingpositioned close to the laser source, such that light from the preheatlight source illuminates an area of the substrate encompassing the areato be annealed. The preheat light source may be angled slightly tocenter the preheat area around the anneal area. Alternately, the preheatlight source may project energy onto the substrate substantiallyperpendicular to the plane of the substrate, with optics used to spreadthe light over a preheat region that encompasses the anneal region. Thepreheat light source may then be advantageously located, with respect tothe laser, such that the preheat area extends further from the annealarea in the direction of the anneal path. The optical assembly mayadditionally be adapted to rotate such that the preheat light sourcemaintains an advantageous position relative to the laser as the annealpath changes direction.

The processing apparatus is preferably configured to translate thesubstrate with respect to the optical assembly by use of a moveablestage of a type known to the art. In operation, the stage positions thesubstrate beneath the optical assembly such that a target area of thesubstrate is exposed to the optical assembly. The preheat light sourcemay be continuously lit, illuminating the substrate with preheat energywhen no anneal energy is present. The continuous preheat energy heatsthe surface of the substrate in an area encompassing the anneal targetarea to at least 600° C. The laser fires one or more pulses at thetarget anneal area. The pulse may be of sufficient brevity that thestage can move continuously, following an anneal path without blurringthe laser pulses. The preheat region moves along the surface of thesubstrate as the stage moves, heating portions of the substrate to thetarget preheat temperature as they approach the target anneal area.Thus, the portions of the substrate immediately adjacent to the targetanneal area are not subjected to damaging thermal stresses due to thehigh thermal gradient at the edge of the target anneal area.

In an alternate exemplary embodiment, the laser may be surrounded by twoto four preheat energy sources spaced around the laser in the opticalassembly. The use of multiple preheat sources allows for uniformpreheating across the entire preheat area of the substrate. Alternately,the laser may be accompanied by two different preheat energy sourcesadapted to illuminate different areas of the substrate. One preheatenergy source may, for example, be adapted to illuminate a circular areaof diameter about 3 cm., which another preheat energy source illuminatesa concentric circular area of diameter about 1.5 cm., concentric alsowith the anneal area. Thus, two preheat areas are formed. The twopreheat sources may deliver similar amounts of energy, such that thesource illuminating the wider area produces a smaller temperature risethan the more focused source. In one embodiment, the preheat sourceilluminating the broad area may heat the area to a temperature of 300°C. or more, while the preheat source illuminating the smaller areawithin the broad preheat area may heat the smaller area to a temperatureof 700° C. or more by virtue of incremental energy. The anneal pulse canthen anneal the substrate by delivering enough energy to raise thetemperature of the anneal area to 1,200° C. or more without melting thesubstrate material.

In another exemplary embodiment, a single energy source may be used. Forexample, a laser may be adapted to produce a single column of light thatmay be used both for preheat energy and anneal energy. Optics, includingmirrors, lenses, filters, and beam-splitters are generally used to tunethe laser light to have a desired polarity or coherency. Such optics mayalso include lenses that defocus a portion of the laser light. Thedefocused portion of the laser light may then be directed to an areasurrounding the anneal area. For example, a laser fitted withappropriate optics may produce a cylindrical beam of coherent lightapproximately 1 mm in diameter. The beam may be directed through a lenshaving a circular non-refractive central portion approximately 0.8 mm indiameter, and an annular defocusing outer portion with an inner radiusof 0.8 mm and an outer radius greater than 1 mm. The portion of thelaser beam passing through the non-refractive portion of the lenscontinues on to reach the substrate, annealing the exposed portion ofthe substrate, while the portion of the laser beam passing through thedefocusing portion of the lens is reduced in intensity and spread over awider area to heat that area to a lower temperature.

While the foregoing is directed to embodiments of the invention, otherand further embodiments of the invention may be devised withoutdeparting from the basic scope thereof.

What is claimed is:
 1. An apparatus for thermally treating a substrate,comprising: a movable substrate support; a first energy source fordirecting annealing energy in a rectangular shape toward a first portionof a surface of the substrate support; a second energy source fordirecting preheat energy in a tapered shape toward a second portion ofthe surface of the substrate support; and an optical assembly housingthe first and second energy sources.
 2. The apparatus of claim 1,wherein the first energy source is a laser and the second energy sourceis a laser.
 3. The apparatus of claim 1, wherein the annealing energyhas a power density of at least 1 W/cm².
 4. The apparatus of claim 3,wherein the preheat energy has a power density of at least 0.1 W/cm². 5.The apparatus of claim 1, wherein the optical assembly further comprisesa first optical tuner to shape the annealing energy and a second opticaltuner to shape the preheat energy.
 6. The apparatus of claim 1, furthercomprising a controller coupled to the substrate support.
 7. Theapparatus of claim 1, wherein the second energy source comprises aplurality of light sources disposed around the first energy source. 8.The apparatus of claim 1, further comprising an actuator to rotate theoptical assembly.
 9. An apparatus for thermally treating a substrate,comprising: a movable substrate support; a first energy source fordirecting annealing energy in a rectangular shape toward a first portionof a surface of the substrate support; a second energy source fordirecting preheat energy in a triangular shape toward a second portionof the surface of the substrate support; and an optical assembly housingthe first and second energy sources.
 10. The apparatus of claim 9,wherein the first energy source is a laser and the second energy sourceis a laser.
 11. The apparatus of claim 9, wherein the annealing energyhas a power density of at least 1 W/cm².
 12. The apparatus of claim 11,wherein the preheat energy has a power density of at least 0.1 W/cm².13. The apparatus of claim 9, wherein the optical assembly furthercomprises a first optical tuner to shape the annealing energy and asecond optical tuner to shape the preheat energy.
 14. The apparatus ofclaim 9, wherein the second energy source comprises a plurality of lightsources disposed around the first energy source.
 15. An apparatus forthermally treating a substrate, comprising: a movable substrate support;a first energy source for directing shaped annealing energy in arectangular shape toward a first portion of a surface of the substratesupport; a second energy source for directing shaped preheat energy in atapered shape toward a second portion of the surface of the substratesupport; and an optical assembly housing the first and second energysources.
 16. The apparatus of claim 15, wherein the first energy sourceis a laser and the second energy source is a laser.
 17. The apparatus ofclaim 15, wherein the annealing energy has a power density of at least 1W/cm².
 18. The apparatus of claim 15, wherein the preheat energy has apower density of at least 0.1 W/cm².
 19. The apparatus of claim 15,wherein the optical assembly further comprises a first optical tuner toshape the annealing energy and a second optical tuner to shape thepreheat energy.
 20. The apparatus of claim 15, wherein the second energysource comprises a plurality of light sources disposed around the firstenergy source